1. Field of the Invention
The present invention relates to an optical communication system in which an optical fiber is used as an optical transmission path.
2. Description of the Related Art
The use of a photonic bandgap fiber (PBGF) as a representative non-communication fiber for transmitting high power light is being extensively studied. In a photonic bandgap fiber, a two-dimensional (2D) Bragg grating is constructed in a cladding region by periodically arranging a medium such as air that has a refractive index different from that of the cladding region. The photonic bandgap fiber transmits a particular operation wavelength from a gap formed by the 2D Bragg grating with respect to a core region that is formed by a hole in the cladding region. A commercial-based photonic bandgap fiber is disclosed in CRYSTAL FIBRE A/S, “AIRGUIDING HOLLOW-CORE REGION PHOTONIC BANDGAP FIBERS SELECTED DATASHEETS HC-1550-02, HC19-1550-01”, [online], [searched on Feb. 8, 2007], Internet (URL: http://www.crystal-fibre.com/products/airguide.shtm).
On the other hand, the possibility of using either one of a holey fiber and a photonic crystal fiber (PCF), which are microstructure optical fibers (MOF) not implementing the photonic bandgap technique, as a communication fiber is being extensively discussed because of the wideband transmission potential thereof. For example, K. Kurokawa, et al., “Penalty-Free Dispersion-Managed Soliton Transmission over 100 km Low Loss PCF”, Proc. OFC PDP21 (2005) discloses transmission characteristics of a dispersion management soliton that is constructed by combining a PCF and a dispersion compensating fiber (DCF), and has a 100 km-long transmission path and a transmission rate of 10 Gb/s.
Meanwhile, the photonic bandgap fiber also has the potential to be used as a communication fiber because of low optical nonlinearity and potential of low transmission loss.
However, as disclosed in the first literature, the operation wavelength of an optical signal that the photonic bandgap fiber uses for communication has such wavelength dispersion and a dispersion slope that a D/S ratio obtained by dividing the wavelength dispersion by the dispersion slope is extremely small. Thus, when an optical transmission path is constructed by using the photonic bandgap fiber, the wavelength dispersion and the dispersion slope cannot be compensated even by using a dispersion compensator of the conventional dispersion compensating fiber. As a result, it is not possible to perform long-haul wideband transmission of an optical signal.